The requirements for them to show up are:
1. the share/drive must be "online" - if there are mp3 files in the same folder that show up, then it must be online, you can look in the admin console under the devices tree at the share device data, it has an online tick box, if ticked then it is online.
2. the files need to be scanned into the data (as audio files, ie make sure you added the file type to the StoredAudio entry), in the file sync section of the admin site, the files must show up with a big tick mark next to them, not as a "drive" icon; and they must not appear in the "missing from disk" section.
3. you either need to be looking in the audio browser using Filename sort mode and navigate to the appropriate folder to see them, or they need to be tagged with meta data such as "Album", etc and be looking in that sort mode instead - note that only mp3 files get their meta data imported from the id3 tags embedded in the file. m4a files do not, and so you either have to tag them manually in the admin console, or only use Filename sort mode and navigate to the correct folder.